1. Field of the Invention
The present invention relates to a thermotropic resin composition capable of giving a shaped article having superior heat resistance, moldability, and mechanical properties and, especially having a balance of an excellent dimensional stability and an excellent wear resistance.
2. Description of the Related Art
In recent years, there has been increased demand for higher performance plastics. Large numbers of polymers with various new performance properties have been developed and supplied to the market. Among them, thermotropic polymers with optical anisotropy which feature parallel arrays of molecular chains, are drawing attention due to their having superior flowability and mechanical properties.
As polymers having anisotropic molten phases, there have been disclosed, for example, the thermotropic polymer comprised of p-hydroxybenzoic acid copolymerized with polyethylene terephthalate (Japanese Unexamined Patent Publication (Kokai) No. 49-72393), the thermotropic polymer comprised of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid copolymerized together (Japanese Unexamined Patent Publication (Kokai) No. 54-77691), and the thermotropic polymer comprised of p-hydroxybenzoic acid copolymerized with 4,4'-dihydroxydiphenyl and terephthalic acid and isophthalic acid (Japanese Examined Patent Publication (Kokoku) No. 57-24407).
These thermotropic polymers, however, have had low mechanical properties in the traverse direction to the machine direction and further have had a large mold shrinkage factor and otherwise extremely great mechanical anisotropy and dimensional anisotropy. Further, thermotropic polymers have molecular chains which are easily oriented and easily form fibriles, so have a large coefficient of dynamic friction and insufficient wear resistance and thus it is extremely difficult to be used in applications requiring large wear resistances.
As a method for reducing these defects, for example, in Japanese Unexamined Patent Publication (Kokai) No. 61-285249, it has been attempted to blend into a thermotropic polymer for making gears a fibrous filler and graphite or another solid lubricant, but while this was effective in improving the mechanical strength, the lubricating properties were not necessarily sufficient.
Further, Japanese Unexamined Patent Publication (Kokai) No. 58-19397 discloses a composition for a lubricating material comprised of oxybenzoyl polyester, natural flake graphite, and polytetrafluoroethylene, but while the coefficient of dynamic friction was small, the amount of wear at a high PV value increased and the impact resistance was reduced.
U.S. Pat. No. 4,889,886 discloses a method of blending into the thermotropic polymer a plate-like powder such as mica, talc, or graphite for the purpose of reducing the anisotropy, but there were still problems in the lubricating properties and this was not sufficient.